Two coils have the same number of circular turns and carry the same current. Each rotates in a magnetic field in a setup similar to the square coil in the figure below. Coil 1 has a radius of 5.5 cm and rotates in a 0.17 T field. Coil 2 rotates in a 0.42 T field. Each coil experiences the same maximum torque. What is the radius (in cm) of coil 2? http://www.webassign.net/CJ/21-21.gif here is what i tried. i found the area of the first coil by using a=(pi)r(squared) =(95.03) next i used the formula t=NAIB for both coils. since i know they both have the same N, I, and t, i can combine the two formulas ending up with AB=ab (cap letters represent 1st coil, lowercase letters represent coil 2) i know all variables except A. now i can find A=38.46. now i can find r of the second coil using A=(pi)r(squared) i found r to be 10.99cm but this is wrong. where did i mess up?